I would like to build this but I do not have the experience to do so with out help. What I am looking for is a 12VDC Var. fan controller with 4 lines suppling at least 60W & 7.5A each with the unit being able to fit into a drive bay in a computer. I have had a little help with this already but need some input as to weather the circuit design is ok#1 or does it need modifications. I am using the LT1083CP in this design. any thoughts comments or suggestions will be of much help also a complete parts list so i can make 2 units controlling 4 lines each.

At 7.5A you'll need a really big heatsink. The regulator will have to dissipate
~53W if the output voltage is 5V and ~15W at 10V. Take a look at the Thermal Considerations section of the LT1083 datasheet to calculate the Heatsink size.

I am not sure if I understood straight. Do you need a fan controller that supplies 7.5 Amps. That is too much current for a couple of fans, indeed.

Wouldn't you prefer a less powerfull version of this regulator (in the National Semicondutor site is suggested the LM1085 or LM1086, that might be cheaper than the LM1084)? Also, you should consider the size of the heatsink to use, since suplying 7.5A requires a big heatsink.

At 7.5A you'll need a really big heatsink. The regulator will have to dissipate
~53W if the output voltage is 5V and ~15W at 10V. Take a look at the Thermal Considerations section of the LT1083 datasheet to calculate the Heatsink size.

I am not sure if I understood straight. Do you need a fan controller that supplies 7.5 Amps. That is too much current for a couple of fans, indeed.

Wouldn't you prefer a less powerfull version of this regulator (in the National Semicondutor site is suggested the LM1085 or LM1086, that might be cheaper than the LM1084)? Also, you should consider the size of the heatsink to use, since suplying 7.5A requires a big heatsink.

The circuit seems to be OK. You can use a 1N4001 diode as well.

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The fans I will be running are rated @3A each 36w to 13.8Vdc brush less, two on each line, I have already bought 7pcs of LT1083CP.
Good point about the heat sink size, I am trying to fit this unit into a computer drive bay so instead of 4 lines per unit maybe i should consider 2 lines per unit due to the dissipation of the heat and the heat sink size.
2 lines per unit will work just fine and can control 4 fans.

Have you looked at PWM control of the fan? It might be better for this
application.

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Yes that might be my next route some one else has also said the same thing but I already have the LT1083CP 7 pcs there quite expensive so i would just like to finish what i have started. The hard thing for me is getting the parts I need for this design, I know very little about any eletric parts etc
At this moment looking to buy parts for 3 units if i can find them all.

There is no change you can make to compensate the voltage drop across the regulator. You can try using a higher voltage power supply to compensate.

A PWM controller might be a good idea to control your fan indeed. Besides having no voltage drop, because it works as a swich, you won't need a such large heatsink.

In its current form, the project requires an heatsink such large that would be impratical. For example, if the regulator regulates to 6V:

P = (13.8V - 6V) x 6A = 46.8W

Only an active heatsink would be practical, and the fan on it should not be fed by the same regulator that is being cooled. And active heatsinks for TO-220 packages are hard to find.

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I just got in the mail today a Mean Well S-250-12 Regulated Switching power supply +12v 18A Continuous with voltage adjustment it puts out over 13 Volts and the size is 6X5 1/2X3 thinking of this for the power source instead of the power supply in the computer.
The Heat sink isue is another story kind of funny I want to build somthing to control heat in my computer but what i am building requires some serious cooling also + puts out heat I am trying to get rid of.
I think the LT1083CP are IC LDO REG ADJUSTABLE 7.5A TO-3P if that makes any difference for which type of heat sink.

Everybody I have encountered says why not go PWM well.....That is a very good question & the only answer i have for that is that i am very inexperienced in the field of electonics & The fan controller plan I have here is the first one that I came across that could handle over 6A per line..I was told at another fourm that if you want anything over 20Watts per channel for a fan controller you would have to make it yourself..And I came across this build and started buying parts for it...
That being said If anybody could show me the way including plans,what parts and a little help putting it together, then I would try PWM circuit. But be aware I want to use the item being built for a computer that fits into a drive bay and can controll 4 fans, There 36Watts, 3Amps, Var 7 to 13.8 VDC Each...If you can come up with a build for me That can handle those fans Via PWM I would be very happy and willing to give that a shot, At this point any help or advice links ideas is so much welcome.